On my iPhone 5 with ios 7 I can choose to automatically download "all" episodes or "most recent". At first glance it sounds obvious what the difference is, but since I've had the "all" setting checked for a while on a podcast that has not started auto downloading (I have enough free space) I have to ask. The app has had plenty of wifi access. The podcast has some added but not downloaded episodes.
Auto downloading the most recent episode only makes sense if it keeps downloading the most recent episode at all points in time from then on. So basically that's the same as "most recent and all future episodes". The "all" setting should then download everything, but what is confusing in that case is that as an explanation of the auto-download settings it says "automatically download new episodes". So is the "all" option "all future episodes" or what? If so there's almost no difference between the two settings.